WASHINGTON, Aug. 14, 2012-- To warn of chemical attacks and help save lives, it's vital to quickly determine if even trace levels of potentially deadly chemicalssuch as the nerve gas sarin and other odorless, colorless agentsare present. U.S. Army researchers have developed a new chemical sensor that can simultaneously identify a potentially limitless numbers of agents, in real time. A paper describing the system has been published today in the Optical Society's (OSA) journal, Optics Letters.
The new system is based on a phenomenon known as the photoacoustic effect, which was discovered by Alexander Graham Bell, in which the absorption of light by materials generates characteristic acoustic waves. By using a laser and very sensitive microphones -- in a technique called laser photoacoustic spectroscopy (LPAS) -- vanishingly low concentrations of gases, at parts per billion or even parts per trillion levels, can be detected. The drawback of traditional LPAS systems, however, is that they can identify only one chemical at a time.
"Photoacoustics is an excellent analytic tool, but is somewhat limited in the sense that one traditionally only measures one absorption parameter at a time," says Kristan Gurton, an experimental physicist at the U.S. Army Research Laboratory (ARL) in Adelphi, Md. "As I started looking into the chemical/biological detection problem, it became apparent that multiple LPAS absorption measurements -- representing an 'absorption spectrum' -- might provide the added information required in any detection and identification scheme."
To create such a multi-wavelength LPAS system, Gurton, along with co-authors Melvin Felton and Richard Tober of the ARL, designed a sensor known as a photoacoustic cell. This hollow, cylindrical device holds the gas being sampled and contains microphones that can listen for
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